GrazianoARN06 - ANRV278-NE29-04 ARI 8 May 2006 15:25 Annu....

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The Organization of Behavioral Repertoire in Motor Cortex Michael Graziano Department of Psychology, Green Hall, Princeton University, Princeton, New Jersey 08544; email: Graziano@princeton.edu Annu. Rev. Neurosci. 2006. 29:105–34 The Annual Review of Neuroscience is online at neuro.annualreviews.org doi: 10.1146/ annurev.neuro.29.051605.112924 Copyright c ° 2006 by Annual Reviews. All rights reserved 0147-006X/06/0721- 0105$20.00 First published online as a Review in Advance on March 15, 2006 Key Words reaching, grasping, avoidance, locomotion, microstimulation Abstract Motor cortex in the primate brain was once thought to contain a simple map of the body’s muscles. Recent evidence suggests, how- ever, that it operates at a radically more complex level, coordinat- ing behaviorally useful actions. Speci±c subregions of motor cortex may emphasize different ethologically relevant categories of behav- ior, such as interactions between the hand and the mouth, reaching motions, or defensive maneuvers to protect the body surface from impending impact. Single neurons in motor cortex may contribute to these behaviors by means of their broad tuning to idiosyncratic, multijoint actions. The mapping from cortex to muscles is not ±xed, as was once thought, but instead is fluid, changing continuously on the basis of feedback in a manner that could support the control of higher-order movement parameters. These ±ndings suggest that the motor cortex participates directly in organizing and controlling the animal’s behavioral repertoire. 105 Annu. Rev. Neurosci. 2006.29:105-134. Downloaded from arjournals.annualreviews.org by CORNELL UNIVERSITY on 06/19/07. For personal use only.
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Contents INTRODUCTION. ................ 106 EVOLVING VIEWS OF MOTOR CORTEX. ....................... 107 ELECTRICAL STIMULATION ON A BEHAVIORAL TIMESCALE. ................... 110 Widespread Use of Long Stimulation to Probe Function. . 110 Spread of Signal Through Connected Networks. ......... 111 MOTOR CORTEX TOPOGRAPHY IS ORGANIZED PARTLY AROUND ETHOLOGICAL CATEGORIES. ................. 112 Defensive Movements. ........... 113 Hand-to-Mouth Movements. ..... Central Space/Manipulation. 114 Reach. ........................... Climbing/Leaping. ............... 115 Other Outward Arm Movements. . 115 Stimulation-Evoked Movements Reflect Movement Repertoire, Not a Single Movement Parameter. .................... Overarching Maps Within Motor Cortex . ...................... 118 NEURONS IN MOTOR CORTEX MAY BE TUNED TO IDIOSYNCRATIC MOTOR OUTPUT PATTERNS . . ........ 120 THE CORTICAL MAP OF MUSCLES IS CONTINUOUSLY REMAPPED BY FEEDBACK. 123 One-to-One Mapping. Many-to-Many Mapping. ........ Feedback Remapping. ............ 125 INTRODUCTION This review describes the cortical motor sys- tem from an ethological perspective. The monkey motor system is emphasized, al- though work on other animals is also con- sidered. Certain actions may be typical of an animal’s motor repertoire, such as reach- ing to grasp an object, manipulating an ob- ject with the ±ngers, putting an object in the mouth, or making defensive movements to block an impending object. How are these behavioral needs reflected in the motor circuitry? One potential risk in studying complex actions is that it might hinder a mechanistic or reductionist understanding of movement control. Traditionally, motor
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GrazianoARN06 - ANRV278-NE29-04 ARI 8 May 2006 15:25 Annu....

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